Kinetic cascade in solar-wind turbulence: 3D3V hybrid-kinetic simulations with electron inertia

Understanding the nature of the turbulent fluctuations below the ion gyroradius in solar-wind turbulence is a great challenge. Recent studies have been mostly in favor of kinetic Alfv\'en wave (KAW) type of fluctuations, but other kinds of fluctuations with characteristics typical of magnetosonic, whistler and ion Bernstein modes, could also play a role depending on the plasma parameters. Here we investigate the properties of the sub-proton-scale cascade with high-resolution hybrid-kinetic simulations of freely-decaying turbulence in 3D3V phase space, including electron inertia effects. Two proton plasma beta are explored: the "intermediate" $\beta_p=1$ and "low" $\beta_p=0.2$ regimes, both typically observed in solar wind and corona. The magnetic energy spectum exhibits $k_\perp^{-8/3}$ and $k_\|^{-7/2}$ power laws at $\beta_p=1$, while they are slightly steeper at $\beta_p=0.2$. Nevertheless, both regimes develop a spectral anisotropy consistent with $k_\|\sim k_\perp^{2/3}$ at $k_\perp\rho_p>1$, and pronounced small-scale intermittency. In this context, we find that the kinetic-scale cascade is dominated by KAW-like fluctuations at $\beta_p=1$, whereas the low-$\beta$ case presents a more complex scenario suggesting the simultaneous presence of different types of fluctuations. In both regimes, however, a non-negligible role of ion Bernstein type of fluctuations at the smallest scales seems to emerge.Comment: 6 pages, 5 figures, final version published in The Astrophysical Journal Letters: Cerri, Servidio & Califano, ApJL 846, L18 (2017

Rape and Other Sexual Violence Against Women and Girls in Armed Conflict: A Legal Look at the Issues

Although historical statistics on the number of victims of rape and other sexual violence during armed conflict can neither be gathered nor relied upon, one may feel safe in saying the number of these types of crimes did not diminish in the 20th century. Nor has the 21st century begun in a manner that gives much hope for a rapid reduction. Sexual violence in armed conflicts has even been said to increase, in spite of the different international conventions signed to eliminate it and in spite of the creation of international courts that have handed down decisions, equating these acts with the worst of international crimes

The third-order law for magnetohydrodynamic turbulence with constant shear

The scaling laws of mixed third‐order structure functions for isotropic, homogeneous, and incompressible magnetohydrodynamic (MHD) turbulence have been recently applied in solar wind studies, even though there is recognition that isotropy is not well satisfied. Other studies have taken account of the anisotropy induced by a constant mean magnetic field. However, large‐scale shear can also cause departures from isotropy. Here we examine shear effects in the simplest case, and derive the third‐order laws for MHD turbulence with constant shear, where homogeneity is still assumed. This generalized scaling law has been checked by data from direct numerical simulations (DNS) of two‐dimensional (2D) MHD and is found to hold across the inertial range. These results suggest that third‐order structure function analysis and interpretation in the solar wind should be undertaken with some caution, since, when present, shear can change the meaning of the third‐order relations

TEACHERS’ PERSPECTIVES, PRACTICES, AND KNOWLEDGE OF RECESS AT THE MIDDLE SCHOOL LEVEL: A MIXED METHOD, CASE STUDY

Prior studies about school recess focuses primarily on the effects and benefits of recess in the context of elementary education. This study focuses on middle school teachers’ perspectives, practices and knowledge of recess, which were collected using both quantitative and qualitative methods. In this case study, 61 middle school teachers participated in an online survey, seven other middle school teachers provided additional insight through a focus group discussion. Data analysis revealed that middle school teachers perceive recess as beneficial overall, but there are also some concerns. Views about recess at the middle school level were not associated with age, gender, level of education, grade level taught, and child dependent responsibilities. While middle school teachers noted benefits of recess, more than half of the participants indicated that recess was not a topic in their professional preparation. However, more than half of the participants indicated that recess deprivation was a topic of discussion with supervisors. Although the practice of recess deprivation for behavioral or academic reasons has been declining, middle school teachers indicated that it does still occur. The middle school teachers in the sample had very limited knowledge of the current trends in educational polices or scholarship about recess. Findings in this mixed-method, explanatory case study indicate that recess should be a topic of conversation among teachers at the middle school level. This study indicated that middle school teachers do not generally receive professional development about the importance of recess. With the increased burden of standardized testing and ever-growing academic demands, teachers understand that students need self-directed time to make their own choices even as they still employ recess deprivation for behavioral or academic reasons. The importance recess at the middle school level must be realized by aligning teachers’ perspectives, practices and knowledge of recess with evidence-based educational research

von Kármán self-preservation hypothesis for magnetohydrodynamic turbulence and its consequences for universality

We argue that the hypothesis of preservation of shape of dimensionless second- and third-order correlations during decay of incompressible homogeneous magnetohydrodynamic (MHD) turbulence requires, in general, at least two independent similarity length scales. These are associated with the two Elsässer energies. The existence of similarity solutions for the decay of turbulence with varying cross-helicity implies that these length scales cannot remain in proportion, opening the possibility for a wide variety of decay behaviour, in contrast to the simpler classic hydrodynamics case. Although the evolution equations for the second-order correlations lack explicit dependence on either the mean magnetic field or the magnetic helicity, there is inherent implicit dependence on these (and other) quantities through the third-order correlations. The self-similar inertial range, a subclass of the general similarity case, inherits this complexity so that a single universal energy spectral law cannot be anticipated, even though the same pair of third-order laws holds for arbitrary cross-helicity and magnetic helicity. The straightforward notion of universality associated with Kolmogorov theory in hydrodynamics therefore requires careful generalization and reformulation in MHD

Inaugural Issue Introduction

The American Graduate School in Paris is introducing its inaugural issue of the Journal of International Relations, Peace & Development Studies. Associated with Arcadia University’s M.A. program in Peace and Conflict Resolution, this journal aspires to encourage discourses that promote non-violence in all aspects of international affairs. Nevertheless, keeping with AGS’s standard of respecting and listening to “the other”, all articles that meet AGS’s high standards of research will be considered for publication, no matter the opinion

Distribution, social structure and habitat use of short-finned pilot whale, Globicephala macrorhynchus, in the Canary Islands

The Canary Archipelago is considered one of the planet’s biodiversity hotspots and the short-finned pilot whale is a key species in need of conservation measures. To address a lack of knowledge, almost 2,000 day-surveys were conducted (1999-2012) resulting in 1,094 short-finned pilot whale sightings. The species was recorded year-round and distributed non-uniformly around the archipelago, with greater densities concentrated in patchy areas mainly on the leeward side of the main islands. A total of 1,320 well-marked individuals were identified, which exhibited a large degree of variability in site fidelity (from core residents to transients). Evidence of an island-associated sub-population and a transient one was found. Longitudinal data were used to infer population structure and estimate abundance, while a spatial modelling approach was used to study spatio-temporal patterns in habitat use, distribution and abundance. Spatial modelling revealed habitat preferences in areas between depths of 1000m and 1500m, and higher densities in the south-west of Tenerife and La Gomera (117 short-finned pilot whales recaptured within the two islands). Abundance of 1,980 individuals (CV = 0.33, 95% CI=1,442 – 2,324) was estimated for the entire archipelago, with higher density predicted during the summer months. Mark-recapture analysis estimated 636 resident individuals (CV = 0.028, 95% CI=602 - 671) in the southwest waters of Tenerife between 2007 and 2009. The social and temporal analyses of the behavioural relationships between pairs of individuals revealed a well-differentiated society with long-lasting and non-random social structure built of constant companions. A hierarchical social system is proposed composed of a population encompassing several clans of pilot whales, each one containing several pods. Nine long-term units were identified with a high degree of association (0.62 - 0.83). This study, the first to provide combined results on distribution, habitat use, and social structure of the species, provides essential information towards the development of recommendations for much needed conservation measures

Solar wind fluctuations and the von Kármán–Howarth equations: The role of fourth-order correlations

The von Kármán-Howarth (vKH) hierarchy of equations relate the second-order correlations of the turbulent fluctuations to the third-order ones, the third-order to the fourth-order, and so on. We recently demonstrated [1] that for MHD, self-similar solutions to the vKH equations seem to require at least two independent similarity lengthscales (one for each Elsässer energy), so that compared to hydrodynamics a richer set of behaviors seems likely to ensue. Moreover, despite the well-known anisotropy of MHD turbulence with a mean magnetic field (B₀), the equation for the second-order correlation does not contain explicit dependence on B₀. We show that there is, however, implicit dependence on B₀ via the third-order correlations, which themselves have both explicit B₀-dependence and also their own implicit dependence through fourth-order correlations. Some subtleties and consequences of this implicit-explicit balance are summarized here. In addition, we present an analysis of simulation results showing that the evolution of turbulence can depend strongly on the initial fourth-order correlations of the system. This leads to considerable variation in the energy dissipation rates. Some associated consequences for MHD turbulence are discussed

The third-order law for increments in magnetohydrodynamic turbulence with constant shear

We extend the theory for third-order structure functions in homogeneous incompressible magnetohydrodynamic (MHD) turbulence to the case in which a constant velocity shear is present. A generalization is found of the usual relation [Politano and Pouquet, Phys. Rev. E, 57 21 (1998)] between third-order structure functions and the dissipation rate in steady inertial range turbulence, in which the shear plays a crucial role. In particular, the presence of shear leads to a third-order law which is not simply proportional to the relative separation. Possible implications for laboratory and space plasmas are discussed